Our main work on visible LEDs has two main aspects.  First, we continue to work to improve the efficiency of blue and green GaN-based LEDs.  Second we work to understand the fundamental causes of inefficiency in GaN-based LEDs:  namely the mechanisms of Shockley-Read-Hall (SRH) recombination and Auger recombination. 

Work on visible LEDs includes work to mitigate efficiency droop by reducing carrier density via low electric field,in the InGaN quantum wells (QWs).  Low electric field in the QWs allows for wider wells and higher radiative electron-hole recombination rates.  We have developed low droop violet and blue LEDs on m-plane and semipolar GaN substrates [link,link] and developed fully field screened blue LEDs [link].  Our current work on green LEDs is basd on c-plane devices on patterned sapphire substrates.  We focus on SRH reduction via improved active region designs and growth conditions.  Our future work will focus on reduced electric field in the QWs.